Mr. Penning on the Physical Geology of East Anglia. 165 



A short description of the geology and physical features of the 

 district was given, and an inference drawn from the varying faunas 

 of the " Crag " that the land was sinking during that era and until 

 after the deposition of the Cromer "Forest-bed." Then Arctic con- 

 ditions began to prevail, and the great glacial subsidence com- 

 menced ; the " lower glacial " beds were formed, and succeeded by a 

 large series of false-bedded gravels and sands, with intercalated 

 patches of unstratified clay. These deposits run up only to a 

 certain level, about 300 feet, never quite reaching the top of the 

 Chalk escarpment, where the overlying Boulder-clay is invariably 

 found resting on the older rock, without any gravel or sand between. 

 The author inferred from this circumstance that after the deposition 

 of the " lower " beds, and as submergence went on, the waters of 

 the North Sea were again united to those of the Atlantic. A strong 

 current was thus set up, which swept down from the north, 

 bringing with it the material of which the gravels are composed, and 

 which is found to consist of pebbles, all derived from the northern 

 and eastern coasts, mixed with flints from the Chalk. The escarp- 

 ment of this formation stood at the time above the water ; but when 

 once sufficiently submerged to admit the water over its lower por- 

 tions, the conditions were altered, the current lost its force, and the 

 deposition of gravel ceased. An occasional iceberg had dropped its 

 load of unstratified clay, which became intercalated with the gravels ; 

 but the greater number of such bergs were quickly swept away to 

 the south. Now the waters had access to a larger area, the forma- 

 tion of gravel was succeeded by that of Boulder-clay, which in the 

 author's opinion, is entirely composed of masses of clay enclosing 

 boulders, brought down and dropped by icebergs in mass, which 

 accounts for its want of stratification. 



This Boulder- clay rests evenly on, and at the higher level over- 

 laps, the " middle glacial " sands ; it then caps the Chalk escarpment, 

 and plunges down into the Cambridge valley, even to the present 

 level of the sea ; but in no instance on or beyond the escarpment 

 does any sand or gravel intervene between it and the older geological 

 formations, although just over the scarp (on the south side) the 

 gravels run up to an elevation of 300 feet. The gravel- forming 

 currents were evidently confined to the seaward side of the Chalk 

 range, and excluded from the Cambridge valley, which is un- 

 doubtedly prce-glacial, and which formed at the time a large inlet, 

 land-locked on every side but one, discharging its waters through the 

 opening now occupied by the estuary of " The Wash." 



In the Cambridge valley there are sheets of river-gravel of recent 

 date, some patches of doubtful age, but not traceable under the 

 Boulder-clay, and an elongated series of gravels at a level of 20 to 

 60 feet above the present level of the Cam. These are in some 

 parts distant from the present course of the river, and present a 

 striking resemblance to glacial gravels ; but as they here and there 

 contain recent shells, and taking into consideration their uniformity 

 of level, the author concludes that they indicate an ancient course of 

 the river Cam. 



